Microstructure based Description of Deformation Behavior of Dual Phase Steel Sheets

Abstract

Dual Phase (DP) steels are Advanced High Strength (AHS) steels that have been widely used in the automotive industries. Generally, DP steels exhibit high strength as well as good formability. Their microstructures consist of hard martensitic islands embedded in soft ferritic matrix. Formability description of this steel grade is challenged, as its damage mechanism was very complex on the micro-scale. The aim of this work was to investigate deformation and fracture behavior of the DP steel grade 1000 by means of a microstructure based Finite Element modelling. Representative Volume Elements (RVEs) were applied to consider effects of various microstructure constituents and characteristics. Individual stress-strain curves were provided for ferrite, martensite as well as transformation induced Geometrically Necessary Dislocations (GNDs) including in the RVEs. The flow curves were based on dislocation theory and partitioning of local chemical composition. Furthermore, the Gurson-Tvergaard-Needleman (GTN) model was used to represent ductile damage evolution in the microstructure. Occurrences of void initiation were observed and damage parameters for RVE simulations were identified. Then, influences of the GNDs, local stress and strain distributions and interactions between phases on crack initiation in the DP microstructure were studied and correlated with experimental results.